1. Field of the Invention
Rotary rock bit bearings must serve in extremely severe conditions comprising very high loads, intense impact, heavy vibration, high temperatures and marginal lubrication. No single material can answer all the requirements imposed by such service equally well.
2. Description of the Prior Art
Engineers have long resorted to composite materials in bearing design to better the capabilities of their machinery. U.S. Pat. No. 356,331, issued in 1887 to Randolf, teaches the use of a soft bearing material and a hard fiber material placed to form alternating axial bars within the bearing surface.
More recently, U.S. Pat. No. 3,235,316 uses bars of nickel silver inlaid in a hard steel bearing. In U.S. Pat. Nos. 4,021,084 and 4,037,300, both issued to Garner and assigned to the same assignee as the present invention, similar inlays are used but of a material harder than the steel bearing. Forming the pockets for the inlays is a difficult procedure, such pockets being generally required in the blind bore of a rotary rock bit cutter. Our invention is directed, in part, at overcoming that problem of physical access.
U.S. Pat. No. 4,248,485 teaches etching some areas of the finished bearing so that those etched areas act softer than unetched areas whereas U.S. Pat. No. 4,232,912 teaches knurling the bearing surface deeply, fusing soft bearing metal to the knurl and finish grinding to expose a finely "gridded" pattern of the two metals. In both of these bearings, a relatively small amount of wear will result in the loss of one of the members of the composite surface. The bearings of a rock bit are expected to continue operating after very heavy wear and often are run to destruction. Bearings made by this new method will retain their composite character through destruction.
A sintered porous metal ring, impregnated with a plastic lubricator, is used in U.S. Pat. No. 4,207,658. This bearing is relatively limited in the amount of impact and load it can survive due to the naturally reduced density of the sintered porous metal.
The present innovation teaches beyond the foregoing state of the art in that the invention provides essentially homogeneous metals of substantial density and dimension to maximize resistance to heavy impact and load.